1. Field of the Invention
The invention relates in general to a sensing method of a scanner, and more particularly, to a high-resolution sensing method for a scanner.
2. Description of the Related Art
A scanner scans a document by incorporating a charge coupled device that detects the light intensity reflected from the document. The charge coupled device may perform a gray-scale scan or a color scan by using a whole row of sensors to scan the light intensity reflected from the document. FIG. 1 shows a schematic drawing of a conventional scanner.
In FIG. 1, a step motor 102 moves a chassis 108 to an optical resolution distance (that is, the width of one row of sensors in the charge coupled device 104). The light emitted from the lamp 106 projects on the document 110, and is then reflected thereby and travels through a mirror 112, a lens 114 to the sensors 116, 118, 120 (R, G, B sensors) in the charge coupled device 104. The detected image signal is then sent to a subsequent circuit (not shown) for signal processing. The step motor 102 then shifts the chassis with an optical resolution distance along the scan direction. According to the above steps, the image signal detected from the next row of the document 110 is sent to the subsequent circuit for signal processing by the charge coupled device 104. Thereby, the image data for the whole document 110 can be obtained.
While scanning the document 110, the optical resolution of the step motor 102, that is, the distance that the chassis 108 is moved by the step motor 102 each time, is reduced to enhance the scan resolution. For example, the motor moves one step in 10 ms with a rotating speed of 100 pps for one time of the optical resolution. If 16 times of the optical resolutions is required, the step motor 102 moves 16 steps in 10 ms with a rotating speed of 1600 pps. Therefore, the higher the resolution of the scanner 100 is, the more the speed of the step motor 102 varies. It is difficult to design a step motor with a large speed variation. The cost thereof is greatly increased.